This invention pertains to a side shifter, and more particularly to such a unit which is especially adapted for mounting on a conventional ITA hook-type lift truck carriage.
As is well known, forklift trucks are widely used in industry for the handling of various kinds of loads. Such a truck has the usual upright telescopic mast on which rides a vertically movable carriage. Various attachments, including lift forks, are made for mounting on such a carriage.
While there are a number of different lift truck constructions available, it is common to find most of these trucks equipped with the well known so-called ITA hook-type carriage. This kind of carriage has a standardized configuration, the specifications of which have been defined by an association of lift truck manufacturers known as the "Industrial Truck Association" (thus the abbreviation ITA), and includes upper and lower spaced horizontal bars joined through suitable interconnecting plates located adjacent the opposite ends of the carriage. The upper edge of the upper bar is formed with a standardized lip for accommodating, through the hook, mounting of various attachments on the carriage.
One kind of attachment which is extremely popular is a so-called side shifter. Such a unit is mounted on a carriage for bi-directional lateral movement, and is intended to carry a variety of different load-handling attachments. With a side shifter operating in place, a truck operator need not be concerned about precise lateral positioning of his truck during load-handling. Operation of the side shifter allows him to correct the lateral position of whatever load-handling attachment he is using.
A problem with known side shifters, however, is that their lateral movements over a period of time produce considerable wear which can require substantial maintenance, and costly down time. For example, in many side shifters there is a relatively high-friction contact that exists between the frame in the side shifter and a carriage carrying the same. Efforts in the past to correct this situation, as by adding rotary bearings, have only been partly successful. While such bearings do yield a lower-friction contact between a side shifter and a carriage, the bearings themselves have proven to be weak points in the construction, particularly with respect to high impact resistance. In other words, in the ordinary operation of a lift truck, there is a considerable amount of bumping and jostling, and impact as a truck is moved toward a load to pick it up. Rotary bearings used heretofore have not well withstood this kind of abuse.
Yet another approach to resolve these problems in the past has involved either the construction of a special carriage with special low-friction high-impact-resistance wear surfaces, or substantial modification of conventional carriages. These have proven to be a very costly approaches, and have not found much favor.
A general object of the present invention is to provide a unique side shifter that features a mounting arrangement which takes all of the above considerations into account in a highly practical and satisfactory manner.
More specifically, an object of the invention is to provide such a unit that can be mounted readily on a conventional widely used ITA hook-type carriage without requiring any modification of the latter.
Another object of the invention is to provide such a shifter in which relatively low-friction contact is obtainable between the frame in the shifter and the carriage.
Still a further object of the invention is to provide a shifter of the type generally outlined in which bearing surfaces between the shifter and the carriage carrying the same are capable of withstanding extremely high impact conditions.
According to a preferred embodiment of the invention, the side shifter includes an upper hook which accommodates a sliding engagement between the shifter and the upper bar in a carriage of the type described. More specifically, this hook is intended to ride on low-friction removable wear shoes that are mounted on the lip in the upper bar of such a carriage. Further featured in the side shifter of the invention are rotary bearings that ride against the front face of the lower bar in the carriage. More particularly, each of these rotary bearings takes the form generally of a segment of sphere, which segment presents a relatively large-diameter spherical bearing surface that affords substantially rolling point contact with the lower bar in the carriage. Each of these bearings is mounted for rotation about an axis which, with the side shifter in place on a carriage, slopes slightly upwardly and rearwardly relative to the horizontal. Each bearing has a large back surface area which rides on a low-friction material that provides an extremely large bearing surface for the handling of any front impact loads on the side shifter.
These and other objects and advantages which are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.